Couple of bugs in Map::insert

See #114, release log:

• b235b97 by @yegor256: Merge pull request #113 from y...
• 17bb4f4 by @rultor: new benchmark results
• cbf18c2 by @Zefick: Dropping the old duplicate on ...
• 484c109 by @Zefick: insert after remove from a ful...
• c08e5ba by @renovate[bot]: Update Rust crate serde to 1.0...
• d915416 by @renovate[bot]: Update Rust crate serde to 1.0...
• edfe03d by @yegor256: Merge pull request #110 from y...
• 9087a76 by @rultor: new version in README

Released by Rultor 1.74.7, see build log